1. Field of the Invention
The present invention relates to an image forming apparatus including a charge eliminator which removes charge from the surface of a photosensitive drum.
2. Description of the Background Art
An electrophotographic type of image forming apparatus, such as a printer or copying machine, generally includes a photosensitive drum, a charger which uniformly charges the surface of the photosensitive drum, an exposure device which forms an electrostatic latent image on the surface by exposing the surface, a developer which forms a toner image by supplying toner to the electrostatic latent image, a cleaner which removes residual toner remaining on the surface of the photosensitive drum after transferring the toner image to a transfer material, and a charge eliminator which removes electrical charge remaining on the surface of the photosensitive drum.
Charge eliminators generally use a light-based charge elimination method based on a LED (Light Emitting Diode). However, in a charge eliminator which employs a point light source such as a LED, there is a problem in that non-uniformity in luminosity is liable to occur when charge elimination light is irradiated onto the photosensitive drum. In particular, there is a tendency for the amount of light to decline in the end portions in the axial direction of the photosensitive drum. Therefore, countermeasures are adopted such as raising the arrangement density of the LED in the end portions of the axial direction, increasing the length of the charge eliminator in the axial direction to greater than the necessary length, and suppressing decline in the amount of liquid in the end portions of the axial direction of the photosensitive drum.
However, if the arrangement density of the LEDs is raised, then costs rise with the increase in the number of the LEDs arranged, and the temperature is liable to rise. Furthermore, if the charge eliminator is increased in length, there is a problem in that the charge eliminator occupies more space than necessary, thus impeding compactification of the image forming apparatus.
Consequently, a conventional image forming apparatus uses a method according to which the irradiation width from the emission end of the light guide member of the charge eliminating apparatus until the photosensitive drum is set to be longer in the end portions in the axial direction compared to the central portion in the axial direction, and the irradiation time of the charge elimination light in the end portions in the axial direction is set to be longer than the central portion in the axial direction. Since the total amount of charge elimination light increases, the longer the irradiation time of the charge elimination light, it is possible to prevent decline in the amount of light at either end in the axial direction.
However, with this method, since the irradiation time is made longer, then it is necessary to set a broader charge elimination light irradiation range than normal, in the end portions in the axial direction. The need to increase the irradiation range in this way may restrict the freedom of the arrangement positions of the other devices, and consequently impedes compactification of the image forming apparatus.